In recent years, electronic equipment has been miniaturized and improved in portability. This has created a growing demand for size and weight reduction of various kinds of electronic components to be housed in the electronic equipment. Accordingly, the electronic equipment has been used in diversified environments, and thus a demand for high reliability with respect to the diversified environments also has been growing.
Against the foregoing background, conventionally, ceramic electronic components have presented a problem of ion migration under high humidity.
Ceramic electronic components are obtained by sintering particles of the micron orders or the submicron orders. Therefore, a sintered body thus obtained may have many minute holes, namely, pores on the surface or in the inner portion. Because of this, when a ceramic electronic component is allowed to stand under high humidity, water vapor penetrates into open pores in an inner portion of a ceramic sintered body, which are open to the surface of the ceramic sintered body. In a pore having a sufficiently small diameter, capillary condensation results in condensing of the water vapor. Among the open pores are open penetrating pores that penetrate between electrodes provided so as to sandwich a ceramic layer therebetween. When a voltage is applied between the electrodes in a state where water droplets obtained as a result of condensation in the open penetrating pores establish a connection between the electrodes, that is, a conductive path is formed by condensation water, an electrode metal represented by an Ag electrode is ionized to cause ion migration. When the ion migration is caused, for example, in the case of a ceramic capacitor, the insulation resistance between electrodes is lowered to cause degradation in electrical characteristics. This problem arises not only in a component with open pores but also in a component with a void (defect) portion that extends from the outside to an area between electrodes.
Conventionally, the following techniques have been adopted to suppress this ion migration, i.e. a technique in which the entire surface of a ceramic sintered body is coated with a synthetic resin, or a technique in which all the pores on the surface of a ceramic sintered body are closed with a synthetic resin or glass.
However, coating the entire surface of the ceramic sintered body with the synthetic resin only serves to retard the penetration of water vapor into open penetrating pores. When allowed to stand under high humidity for a long time, the water vapor diffuses through the synthetic resin to penetrate into the open penetrating pores. Then, the water vapor is condensed by capillary condensation. This phenomenon is accelerated and thus becomes likelier to cause condensation under high temperatures and humidity. Water droplets obtained as a result of the condensation form a conductive path between electrodes to cause ion migration, thereby causing variations in electrical characteristics of a ceramic electronic component, which has been disadvantageous.
On the other hand, when all the pores on the surface of the ceramic sintered body are closed, the synthetic resin and the glass are used in the following manners, respectively. In the case of using the synthetic resin, a technique is employed in which the ceramic sintered body is impregnated with a mixed solution of a resin and a solvent and then cured. In the case of using the glass, a technique is employed in which a glass paste is printed and baked. When these techniques are employed, cross-linking or curing of the synthetic resin is caused, or the glass is reduced in volume when melted and sintered. This makes it very difficult to close all the pores. Even when all the pores are closed successfully, it is impossible to fill the entire space in the pores. Instead, voids are formed in the pores, or the pores are coated with a film. In this case, water vapor penetrates into the pores via the voids or is diffused to permeate through the coating film into the pores in an inner portion of the ceramic sintering body. In some cases, when allowed to stand under high humidity for a long time, the water vapor is condensed in the inner portion, so that a conductive path is formed between electrodes to cause ion migration, which has been disadvantageous.
In order to form the synthetic resin and the glass so that no voids are formed in the space in the pores, a method also is employed in which a synthetic resin component of the solution with which the ceramic sintered body is impregnated and a glass component of the glass paste are increased in concentration. However, with increased concentration, the solution and the glass paste are increased in viscosity. This makes it very difficult to impregnate all the pores on the surface of the ceramic sintered body with the solution and the glass paste. Even when the solution is allowed to permeate through all the pores on the surface of the ceramic sintered body successfully, it is impossible to allow the solution to permeate through the pores in the inner portion of the sintered body. As described above, when a technique is limited to a simple process in which all the pores on the surface of the ceramic sintered body are closed with the synthetic resin, water vapor is diffused through the synthetic resin to penetrate into the inner portion of the ceramic sintered body. This causes ion migration, thereby causing variations in electrical characteristics, which has been disadvantageous. On the other hand, when the entire surface of a ceramic sintered body is coated with glass completely, while water diffusion and penetration can be prevented, diffusion of the glass into ceramic is caused when the glass is baked, thereby causing variations in characteristics. Because of this, in many cases, this technique cannot be employed from a structural standpoint.